Atypical cells in a breast biopsy -27 years old

My daughter is 27.  She has a cyst that increased a cup size in two weeks time.  She has had a needle biopsy of the cyst and had it aspirated. They also found a hard area behind the cyst that they also took a biopsy of.  Her results came back with atypical cells.  I had stage one breast cancer at 44.  How prevalent is cancer in a woman this young.

[Cleveland Clinic]

Dear Naomi56,  Cancer is not that common in younger women but it does occur.  A finding of atypical cells would likely lead to further evaluation to be sure the area of concern has been fully evaluated.  

[Naomi56]

Additional tests reveal cancer